1. Field of the Invention
The present invention relates to the manufacturing of a semiconductor device, and specifically to a metal-polishing composition used in the wiring process of a semiconductor device for planarizing the semiconductor device, and a chemical-mechanical polishing method using the same.
2. Description of the Related Art
In the development of semiconductor devices, as represented by a large-scale integrated circuit (hereinafter, referred to as LSI), densification and enhancement of integration by poly-lamination of and formation of finer wiring have recently been demanded for the purpose of miniaturization and higher speed. For these purposes, a variety of techniques such as Chemical Mechanical Polishing (hereinafter, referred to as CMP) have been used. This CMP is an essential technique when surface flattening of processed films such as an interlayer insulating film, plug formation, formation of embedded metal wiring, or the like is carried out, and removes an extra metal thin film during substrate smoothing and wire formation.
A general CMP method involves sticking a polishing pad on a circular polishing platen, soaking the surface of the polishing pad with a polishing liquid, pushing the surface of a wafer on the pad, rotating both the polishing platen and the wafer under conditions of a specified pressure (polishing pressure) from the back surface side of the wafer, and flattening the wafer surface by means of generated mechanical friction.
The metal polishing liquid used for CMP commonly contains an abrasive (e.g., alumina, silica) and an oxidizing agent (e.g., hydrogen peroxide), and is considered to oxidize a metal surface with the oxidizing agent, and polish the surface by removing the oxide film with the abrasive.
However, when CMP is carried out using such a metal polishing liquid, problems may occur such as polishing scratches, excessive polishing of the entire polished surface (thinning), a phenomenon in which the polished metal surface is not planar and only the center is more deeply polished to form a dish-like hollow (dishing), and a phenomenon in which an insulator between metal wirings is excessively polished and a plurality of wired metal surfaces form a dish-like concave portion (erosion).
Conventionally, tungsten and aluminum have been generally used as metals for wiring in interconnection structures. With the aim of higher performance, however, LSIs have been developed in which copper having a wiring resistance lower than those of these metals is used. The Damascene method is known as a method of forming wiring with this copper. Additionally, the dual Damascene method has been widely used which involves simultaneously forming both a contact hole and a wiring groove in an interlayer insulating film, and embedding a metal in the both of these. A copper target having a high purity of five nine (99.999%) or more has been commercially available as a target material for the copper wiring. However, with recent formation of finer wiring aimed at further densification, improvements in the electrical conductivity, electronic properties and the like of copper wiring have become necessary. As such, the use of a copper alloy made by addition of a third component to highly pure copper has begun to be investigated. At the same time, high-speed metal-polishing methods capable of high productivity without contamination of these highly minute and highly purified materials are demanded. Polishing of a metal of copper readily generates the above-mentioned dishing, erosion or scratches due to its particular softness, and thus a polishing technique with higher precision is required.
Recently, for the purpose of increased productivity, the size of a wafer during LSI production has been increased more and more. Presently, a wafer having a diameter of 200 mm or more is widely used, and a wafer having a size of 300 mm or more has begun to be manufactured. With such an increase in the size of a wafer, a difference in polishing speed between the center portion and the peripheral portion of the wafer is easily generated, and demand with respect to uniformity in polishing within the wafer surface has become increasingly severe.
For copper and copper alloys, a metal polishing liquid which contains no abrasive and contains hydrogen peroxide, malic acid, benzotriazole, ammonium polyacrylate, and water is proposed in, for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-127019. However, a chemical polishing method by means of chemical dissolution alone still has a major problem with respect to planarity of the polished surface because of excessive shaving in a concave portion, or dishing, in comparison with CMP in which a metal film of a convex portion is selectively subjected to chemical-mechanical polishing.
When using copper wiring, a dispersion preventing layer, called a barrier layer, is usually provided between the wiring portion and an insulating layer for the purpose of preventing dispersion of copper ions into an insulating material, and the barrier layer is made of one layer or two or more layers selected from TaN, TaSiN, Ta, TiN, Ti, Nb, W, WN, Co, Zr, ZrN, Ru and CuTa alloys. However, since these barrier materials themselves have electrical conductivity, the barrier material on the insulating layer must be completely removed for the sake of preventing error generation due to leaked current or the like. This removing processing is attained by a method similar to bulk polishing of a metal wiring material. In bulk polishing of copper, dishing is particularly liable to occur in a wide metal wiring portion, and therefore, it is desirable to adjust the amounts of polishing removal in the wiring portion and in the barrier portion for the purpose of achievement of final flattening. Because of this, a polishing liquid for barrier polishing desirably has the optimal polishing selectivity for copper/barrier metal. In addition, because the wiring pitch or wiring density differs in a wiring layer of each level, it is still more desirable to be capable of adjusting, as appropriate, the above-mentioned polishing selectivity.
Chemical-mechanical abrasive compounds used for CMP commonly contain, as discussed above, polishing particles such as alumina and silica. Accordingly, it is considered that the mechanical polishing force of the compounds is strongly exerted on the convex portion and weakly exerted on the concave portion on the surface, whereby the polishing rate is higher in the convex portion than in the concave portion, which results in planarization of the surface.
Furthermore, when a polishing liquid containing solid abrasives is used, there are problems concerning cost with respect to a washing process with usually follows the polishing process for removing residual polishing liquid on the semiconductor surface, such as the washing process being complicated and the necessity for sedimentation separation of the solid abrasives in the treatment of the liquid after washing (waste water).
As one means to solve these problems, for example, a metal surface polishing method by means of a combination of a polishing liquid that does not contain an abrasive and dry etching is disclosed in Journal of Electrochemical Society, Vol. 147, No. 10, pp. 3907-3913, 2000, etc. According to these methods, the metal films of the convex portions of a semiconductor substrate are selectively subjected to CMP, and metal films remain in concave portions, whereby a desired conductive pattern is obtained. Since CMP proceeds by means of friction against a polishing pad that is mechanically much softer than conventional materials containing solid abrasives, generation of scratches is reduced. Due to a decrease in mechanical polishing force, however, these methods have a disadvantage in that it is difficult to obtain a sufficient polishing speed.
On the other hand, a polishing agent containing an abrasive has a characteristic of obtaining a high polishing speed. In general, fine particles of inorganic oxides such as silica, alumina, ceria, titania, and zirconia are used as abrasives. These abrasives are known to have both advantages and disadvantages. For example, silica is comparatively soft and thus hardly generates scratches, but the polishing speed thereof is not sufficient. On the other hand, alumina is hard and offers a high polishing speed, but it is liable to generate scratches and causes a problem of instability over time due to particle aggregation. Further, although a composite abrasive in which surfaces of silica are covered with alumina is disclosed in, for example, JP-A No. 2003-197573, it does not sufficiently exhibit the advantages of silica and alumina.